Some disorders of the gastrointestinal (GI) tract are difficult to detect and present detection systems having a camera sensor incorporated into a swallowable pill are often not sufficiently accurate to allow early identification of a problem. Bleeding in the GI tract is a common symptom of several diseases such as Crohn's disease, ulcerative colitis, ulcers and cancer. Bleeding in the GI tract can go unnoticed until it reaches a scale where other symptoms appear, e.g. anaemia, or if fresh blood appears in the stool. By this time, the disease has usually reached an advanced stage. In the case of bowel cancer, polyps often bleed before they become cancerous. Consequently, if they can be detected early, the polyps can be safely removed and the cancer treated successfully. There are known faecal occult blood (FOB) tests, for testing for the presence of blood in stool. These are generally based on the peroxidase-like behaviour of haemoglobin or are based on immunoassays.
One known FOB test uses a guaiac resin impregnated card. Guaiac resin (extracted from trees) changes colour in the presence of oxidising agents. Such tests utilise the fact that haemoglobin catalyses the oxidation of the phenolic compound in guaiac resin (alpha guaiaconic acid) by hydrogen peroxide to form a highly conjugated blue quinone compound. In guaiac-based FOB tests samples of stool are spread by the patient on a card impregnated with guaiac resin. Two samples from each of three stools are typically required to be collected before the card is sent for analysis. In the analysis laboratory, a hydrogen peroxide developer solution is applied to the card and, if blood is present in the sample, a blue-green colour is the result.
The FOB test described above is of use in screening tests, where patients receive the test through the mail, or from their local doctor, take and apply their own samples to the card, and return the card to the laboratory for analysis. The take-up of such tests is variable, particularly amongst the elderly, and amongst people from certain ethnic or social backgrounds, probably due to the unpleasant nature of taking the samples and applying them to the cards.
As an alternative to the screening cards described above, WO 2006/085087 discloses a sensing apparatus, which includes a swallowable pill, having an array of sensor elements, where each element is a biological sensor for detecting the presence of the same analyte in the environment in which the sensor array is to be deployed. Activation of a sensor element in the array allows analyte present in the environment of the sensor element, such as haemoglobin, to catalyse a chemical reaction between a first reagent, such as alpha guaiaconic acid, and a second reagent, and the detection of the chemical reaction by the sensor element determines the sensor element output. The first reagent is typically contained within a reagent space of the sensor, which is covered, and may be made available, as required, by removal of that cover to expose the reagent to the local environment.
The provision of a sensor having a reagent space with a removable cover complicates the design of the swallowable pill. There is need for an alternative sensor having a design that is easier to operate and easier to fabricate.
The present invention is particularly useful in systems where a swallowable capsule with a sensor is swallowed by a patient and transmits gathered data from inside the body to a base station outside the body via a radio or other communication link. However it is not limited to this application and may also be used on a sensing device designed for implantation into the human body. It may also be used in topical application, e.g. in wound dressings. It may also be used with animals, especially but not limited to agricultural livestock, such as cattle sheep and pigs. Application not only to mammals, but also to non-mammals, e.g. fish at fish farms, would also be possible.
The present invention also finds use in the analysis of samples taken from a subject. An analytical device with a sensor may be used for rapid, qualitative measurements of a sample, especially with a view to determining the presence of a protein, such as haemoglobin, at physiological or clinical levels.
Whilst some aspects of the present invention relate to apparatus such as swallowable pills, other aspects provide improved sensors for use in the analysis of biological samples. These sensors may be used as alternatives to those sensors, such as the cards discussed above, that are currently on the market. The sensors of the invention provide faster results without the need for a suitably experienced analytical technician.